The present invention generally relates to improved crane operation. More specifically, the invention relates to an electronic control system that prevents the crane's operator from overstressing the lattice boom when operating the hydraulic spotter and provides continuous, self-compensation against spotter hydraulic system leakage (hydraulic drift) caused by the pile lead being twisted when continuous-flight-auger (CFA) drilling or pile driving.
Pile driving and CFA drilling are well-established methods that have changed very little in basic principle since their introduction many years ago, as described in U.S. Pat. Nos. 3,550,693, 3,888,317 and 4,102,094, each incorporated by reference herein in its entirety. The crane's operator requires considerable skill if major equipment damage is to be prevented when pile driving at acute angles. This is of particular importance during sideways battered piles. Incorrect operation can cause catastrophic failure through twisting and/or side loading of the crane's lattice boom if the spotter is not operated in the correct manner. Lattice booms are generally designed to work with compressive loads.
A spotter is a hydraulically-operated mechanical arm attached between the front end of a mobile crane and a pile lead. The spotter is designed to hold the pile lead at the proper inclination and handle overhanging loads while pile driving, and reactive torque while CFA drilling. The pile lead is generally attached to the top of the crane's lattice boom by an upper two-axis (x and z) pivoting boom box. The hydraulic spotter is designed to swing, extend and retract the lower portion of the pile lead, while the upper two-axis boom box allows movement between the pile lead and the crane's lattice boom.
Hydraulic spotters are generally manual or a automatic in operation. Automatic spotters feature a hydraulic steering system that keeps the pile lead's front attachment face (flange) at 90 degrees to the crane's boom centerline while the spotter is being operated (swung from side to side), thereby preventing excessive stressing to the crane's lattice boom. This system can, over time, get out of phase (due to hydraulic oil leaking past the cylinder's packing and valves) and is unable to self-compensate. The hydraulic system must be bleed manually to bring the system back into phase.
Sliding frames or “sliders” may be used to attach pile driving hammers and auger drilling attachments to the front face or flange of the pile lead. The attachments may be raised and lowered by a steel cable and winch, powered by the crane.
The following problems have, until now, caused considerable damage to the crane's lattice boom and the pile lead's mechanical structures when using the standard two-axis upper boom box and spotter with manual and/or self-steering control:                1. The pile lead is not in constant alignment with the crane's boom tip when operating the spotter, as the crane's operator is unable to properly judge the pile lead's alignment with the crane's boom tip. This is most common during sideways batters when the spotter is swung out from under the lattice boom.        2. The spotter's hydraulic system drifts over time, given normal oil leakage, causing the pile lead to twist and/or side-load the crane's lattice boom.        3. The crane's boom is subjected to twist and/or side loading caused by torque reaction when CFA drilling or pile driving at acute angles.        
Resulting twisting or side loading of the crane's lattice boom caused by these conditions can cause catastrophic failure, personal injury and even death.
Accordingly, it would be advantageous to provide apparatus and a method for improving crane operation to solve the above-referenced problems, and the present invention is believed to do so, as explained below.